1. Field of the Invention
The present invention relates to a variable resonator capable of reducing noise due to air intake noise originating from an engine of an automobile, etc., over a wide operating range.
2. Description of the Related Art
Conventional resonators are configured such that a tubular member branches off perpendicularly from an air intake duct, and an end surface of the tubular member opens onto a resonance chamber.
In conventional resonators configured in this manner, since the length of a communicating channel between the air intake duct and the resonance chamber is constant, resonance frequencies are fixed uniformly, and damping effects can be achieved only at those specific resonance frequencies.
If an attempt is made to handle a wide range of frequencies of air intake noise that change over a wide operating range from low speeds to high speeds using conventional resonators of this kind, it is necessary to provide a plurality of resonators manufactured so as to have different resonance frequencies by changing the length of the communicating channel between the air intake duct and the resonance chamber, and one problem has been that installation space in the engine compartment is increased thereby.
In view of these conditions, a first variable resonator has been proposed that is configured such that an outer tubular member is branched off perpendicularly from an air intake duct, an end surface of the outer tubular member opens onto a resonance chamber, and an inner tubular member is disposed slidably along an inner wall of the outer tubular member. (See Patent Literature 1, for example.) In this first conventional variable resonator, the resonance frequencies are made variable by sliding the inner tubular member along the inner wall of the outer tubular member so as to change the amount of inner tubular member projecting outward from the outer tubular member, in other words so as to change the length of the communicating channel between the air intake duct and the resonance chamber.
A second variable resonator has also been proposed that includes: a case body having a resonating portion communicating with an air intake duct through a tubular neck portion, the resonating portion being formed so as to have a circular container shape aligned with the neck portion; a cylindrical fixed tube fixed concentrically inside the case body and connecting to the neck portion an annular passage formed between the case body and the fixed tube; and a movable member moving through the annular passage by sliding in contact with an inner peripheral surface of the case body and an outer peripheral surface of the fixed tube. (See Patent Literature 2, for example.) In this second conventional variable resonator, the neck portion is made to communicate inside the fixed tube through the annular passage by arranging a plurality of communicating apertures circumferentially on the fixed tube. Thus, the resonance frequencies are made variable by opening and closing the communicating apertures of the fixed tube by sliding the movable member so as to change the length of the communicating channel between the air intake duct and the fixed tube.
Patent Literature 1: Japanese Patent Laid-Open No. SHO 59-105958 (Gazette)
Patent Literature 2: Japanese Utility Model Laid-Open No. HEI 03-89975 (Gazette)
In the first conventional variable resonator, the length of the communicating channel between the air intake duct and the resonance chamber is changed by moving the inner tubular member rectilinearly in a direction perpendicular to the air intake duct so as to change the amount of inner tubular member projecting outward from the outer tubular member. Thus, in order to widen the range of resonance frequencies, it is necessary to increase installation space for the resonator to allow for a long range of movement of the inner tubular member, and interference with other parts has been a problem.
In the second conventional resonator, because it is necessary to form the resonating portion so as to have a circular shape, one problem has been that the shape of the resonating portion cannot be changed to avoid interference with other parts, placing constraints on layout.